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Fix Your Toyota Prius P0420 Catalyst Efficiency Code For Less Than $20

I am never a fan of "quick fixes" but I will have to say this proved me wrong. Here is what I did to fix an expensive problem for less than $20.

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As an automotive professional, there is nothing that gets me more riled up than a "quick fix" or "mechanic in a bottle." I have found with my years in this industry; there are seldom repairs that can be solved by pouring a solution into your gas tank, and then you get 1000 horsepower. (This, of course, is an exaggeration, but you get the gist of it)

I have not yet once found a quick solution to solve a long term problem, until today. Not only did this $20 fix work, but it has proven itself now for many cycles.

P0420 Catalyst System Efficiency Below Threshold - On Your Toyota Prius
Now, if you are one of those unlucky people who have had their catalytic converter stolen, I am sorry. This repair will not fix your P0420; you will need to replace what is missing, your catalytic converter.

If you Prius still has the catalytic converter and you get the code, you need to know what it means before heading to your local muffler shop for a repair.

Toyota Prius Catalytic Converter

When the P0420 trouble code appears, your catalytic converter is not performing the way it used to. The rear O2 sensor monitors the converter and the amount of oxygen that is stored inside. If the converter cannot keep enough oxygen, the sensor will detect that and set the trouble code.

The reason that our Prius converters stop working is for several reasons. One of those reasons is because they start to consume copious amounts of engine oil. This action then coats the substrate inside the converter, and it cannot "fire off" and work as it needs to.

There are other reasons for converter failure, but for the sake of getting to fixing the converter, know they exist.

So, if the converter gets coated with garbage, is it possible to clean it off? The answer is yes, but. The but part comes from knowing if your catalytic converter substrate is melted or not, which without physically looking at it, you would not know.

The only way you would know if you know if your substrate is broken is by hitting it and seeing if it rattles. At that point, if it did rattle, do not bother with trying this repair either; you will need a new converter.

How To Fix A Fouled Catalytic Converter For Less Than $20
Now I have to give credit where credit is due, and I did not come up with this repair. I did, however, confirm that it does work. The idea came from another Prius owner Matt Day who swore it worked.

He showed the group a can of Turbo and Intake Valve cleaner by CRC. He said he followed the instructions and never had the code reset. He even checked the system monitors saying they had all completed and passed.

I was blown away that a can of cleaner could make such a claim, so I had to try it myself. Lucky for me, I have a test Prius with a P0420 and needed to get a replacement converter, or so I thought. For less than $20, it was worth a shot.

CRC Turbo and Intake Valve Cleaner

After grabbing a can of CRC Turbo and Intake Valve Cleaner, I read the instructions. With Prius, it would be a challenge to keep it at 2,000 RPM, so I hooked up my Techstream and monitored engine speed.

I was able to keep it between 2,000 and 2,500 RPM spraying short bursts of fluid in through the intake manifold until the can was gone. I revved (as much as I could) the engine three times, then shut it off to soak for the 1 hour as stated on the can.

After an hour was up, I fired up the car and drove at highway speeds for 15 minutes, as indicated by the directions. No codes. I checked my readiness monitors. Catalyst monitor was complete and had passed.

To be sure, I then let the car sit overnight to allow the final EVAP monitor to run. I then drove the car all day—no codes, not P0420, nothing. Matt, you were right.

Did the process work? Yes, it did. Is, is going to last? I have no idea. I put over 150 miles on the car since the repair with no sign of trouble. The thing is this, though. What if this got you through another year of smog? For $20, it is undoubtedly worth the time to try it.

I will update this story if any new news comes up or if it fails. The thing is, do not go getting a new cat converter without first trying this process. If you want to know exactly what it is, you can find a link here.

Thank you all so much for reading. Please feel free to ask questions. Find me on Twitter at The Hybrid Guy for faster answers. Have a great week, everyone.

Check out this wild story about why you need to stop asking what engine oil to use in your car.

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Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporters.

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Lee Kresge (not verified)    November 24, 2020 - 12:07PM

I had the same luck with two gas treatment products I got on Amazon: CataClean and OxyClean. The CataClean worked at the end of the 4-5 gallon treatment and kept my CEL out for a couple hundred miles. Certainly long enough to pass emissoins test. Well, I waited too long and my CEL came back on. I tried a can of OxiCat in ~5 gal of gasoline and my CEL light has been off for 2-3 tanks.

My luck had it that my hybrid battery would call it quits at 349,655 miles, 3 days before my scheduled NYSI was to be performed. If my baby didn't have cancer, I would go through the trouble/expense of replacing the battery. Living in the rust belt does have it's drawbacks...

Jerome King (not verified)    November 16, 2021 - 4:17PM

@Peter, do you have an update on how long the CRC effect lasted? Did you get the P0420 again? and when did it show up? If the P0420 did not come back, are you doing a CRC treatment every year? Thx. I had the same issue with my 08 Prius and the CRC treatment has worked so far... only 250 miles though so I am wondering if it will last and how long.

Jerome (not verified)    November 18, 2021 - 12:48PM

@Peter, do you have an update on how long the CRC effect lasted? Did you get the P0420 again? and when did it show up? If the P0420 did not come back, are you doing a CRC treatment every year? Thx. I had the same issue with my 08 Prius and the CRC treatment has worked so far... only 250 miles though so I am wondering if it will last and how long.

Travis (not verified)    June 24, 2022 - 4:14PM

Is there any harm in continuing to drive my Prius with the cat code lit? I live in an emmisions free county/area and don't need it tested for as long as I'm here. Pls do let me know. Thx!

Hoss (not verified)    June 29, 2022 - 5:47PM

In reply to by Travis (not verified)

I have been going to battle with my 08 Prius with 438,000 miles on in and the 0420 and 0421. I am fortunately able to tell you that running with the codes can, in the long run, mess your car up. I noticed that the oil was being consumed at a higher than average rate. Even with the miles on it. I bought a cheap aftermarket Cat Conv and put it on and it was not as long as the oem one so I had to make a spacer. One thing that I noticed was the power was very lacking due to the A/F ratio being off due to the code. So yes you can drive it but no, it will not be good on the car in the long run.

Jerome (not verified)    June 3, 2023 - 8:18AM

In reply to by Eric Ramirez (not verified)

If I recall correctly, I haven't done this in a couple of years now. I think you remove the air filter compartment and it should be there on the left. Check Youtube for throttle body cleaning.

Peter (not verified)    October 20, 2023 - 1:02AM

Almost too good to be true but got me through smog!!!!!

2005 Prius Gen. 2. 225k miles.

If you try this a few things seem to affect it.

A good run on the freeway really working the engine made the 420 code go away for a while.

Cool engine brought the code back.

I had to time my trip to the smog station just right.

Totally worth it in California where a new cat costs more than the car cost me!!!

Peter Vroom (not verified)    October 23, 2023 - 6:49PM

In reply to by Peter (not verified)

Update. The code came and went a few times over the next few days. Check engine came on. Reset the code again and for several days the check engine light (permanent code) has been off but there is a temp 420 in the system.

The car uses about 1 litre/qrt of oil per 5k miles. I’m wondering if that is what’s blocking the cat a little such that this product helps. Ie the problem is not the cat itself but oil.